DE102016205913A1 - Biaxially oriented polyester film for metal lamination - Google Patents

Abstract

The invention relates to a multilayer biaxially oriented polyester film comprising a base layer B, an amorphous cover layer A and a further cover layer C, this polyester film being suitable for lamination with metal sheets. In particular, the invention relates to a polyester film containing in the base layer (based on the mass of polyester) from 2 to 15 wt .-% isophthalate-derived units and in the amorphous layer A contains more than 19 wt .-% isophthalate-derived units and which is provided on the cover layer A with a silane-based coating. Furthermore, the invention relates to a method for producing these films.

Description

Field of the invention

The invention relates to a multilayer biaxially oriented polyester film comprising a base layer B, an amorphous cover layer A and a further cover layer C, this polyester film being suitable for lamination with metal sheets. In particular, the invention relates to polyester films, which are preferably made of antimony-free polyesters and contain radical scavengers. In one embodiment of the invention, this relates to a polyester film containing in the base layer (based on the mass of polyester) 2 to 15 wt .-% isophthalate-derived units and in the amorphous layer A more than 19 wt .-% isophthalate-derived Contains units and which is provided on the cover layer A with a silane-based coating. Furthermore, the invention relates to a method for producing these films.

background

Polyester films have a variety of applications due to their excellent optical and mechanical properties. One field of application is sheet metal lamination, in which the polyester film is laminated to a metal sheet.

Lamination is used to protect the sheets against corrosion or for decorative purposes (printing). In the case of metal cans, which are produced from foil-laminated sheets, the film laminated on the inside serves as a barrier between packaged goods and metal. On the one hand, the film prevents, on the one hand, the diffusion of corrosive constituents of the packaged goods to the metal and, on the other hand, the diffusion of corrosion products into the packaged goods. A laminated on the outside film serves in addition to the corrosion protection usually decorative purposes.

Usually sheet metal foil laminates are produced by, for example, bringing together a multi-layer sealable film with a sheet heated to a high temperature. Another possibility is to stick the film on the sheet by means of an adhesive. Here, either solvent-based adhesives or hotmelts are used.

The films of the present invention are particularly suitable for lamination at high temperature to aluminum. Due to the fact that the melting point is lower than that of a (pure) PET film, the film according to the invention can be melted in the laminate with aluminum without negatively influencing the mechanical properties of the aluminum. By melting the film, the laminate can be deformed without causing cracks in the film.

State of the art

In the GB-A-1 465 973 describes a thick coextruded, two-layered polyester film, one layer of isophthalic and terephthalic acid-containing copolyesters and their other layer of polyethylene terephthalate. About the adhesion of the film to metal can be found in the document no information. Due to the lack of pigmentation, the film can not be wound and can not be processed further.

In the EP-B-312 304 For example, a process for laminating a multilayered polyester film to metal is described. For this purpose, the sheet is preheated, the film is laminated and then melted and quenched. In order to achieve a good deformability of the laminated sheet, process temperatures of at least 260 ° C are called. The polyester film consists of an inner non-crystalline layer having a melting point less than 250 ° C and an outer crystalline layer having a melting point above 220 ° C. The polyester of the non-crystalline layer is typically a copolyester of 80% ethylene terephthalate and 20% ethylene isophthalate. Corresponding films in the examples have a thickness of 15 μm.

In the EP-B-474,240 Polyester films are described for sheet metal lamination, which consist of a copolyester having a melting point between 210 and 245 ° C. In the examples, copolyesters having an isophthalic acid content of 9 to 12 mol% are mentioned. The laminated sheets are processed into deep-drawn cans for food packaging. The films mentioned are monofilms without sealing layer and show too little adhesion to aluminum.

In the EP-A-586 161 describes single-layer polyester films for lamination on sheet metal, a copolyester having a melting point between 210 and 245 ° C and two different sized particles having a mean diameter of 0.05 to 0.6 microns and 0.3 to 2.5 microns. The laminated sheets are processed into deep-drawn cans for food packaging. The films should have a good heat resistance and do not change the taste of the filling.

task

The prior art films are disadvantageous because they do not exhibit sufficient adhesion at the reflow temperature suitable for aluminum. Inadequate adhesion is particularly noticeable in contact with food or its substitutes and during pasteurization or sterilization in contact with these products. In addition, they have too low ductility and insufficient corrosion resistance.

The object of the present invention was to find a polyester film which is suitable for lamination on aluminum. The film should show good adhesion in the laminate and offer high corrosion protection for the aluminum. Furthermore, the laminate should be suitable for direct contact with foodstuffs and should retain mechanical stability even with prolonged exposure to heat and at the same time exhibit low antimony migration values.

Solution of the task

The object is achieved by providing a coextruded, multilayer, biaxially oriented polyester film having a crystalline base layer B, an amorphous top layer A and a crystalline top layer C. The amorphous cover layer A preferably carries a silane-containing coating.

detailed description

The polyester film according to the invention consists of polyester, additives and preferably a coating.

base material

The base layer of the film of the invention is crystalline and has a melting point of less than 250 ° C, preferably less than 245 ° C. Due to the crystallinity, the film has good mechanical strength, can be produced economically and is easy to process.

In one possible embodiment, the polyester of the base layer B of the film consists of at least 85% by weight, preferably at least 90% by weight, particularly preferably at least 92% by weight, of ethylene terephthalate-derived units and from 2 to 15% by weight. , preferably 3 to 10 wt .-%, particularly preferably 4 to 8 wt .-% of ethylene isophthalate-derived units (in each case based on the total mass of polyester). The sum of ethylene terephthalate-derived units and ethylene isophthalate-derived units is at least 95% by weight of the polyester.

The remaining units derived from carboxylic acids or alcohols originate from other aliphatic or cycloaliphatic diols or dicarboxylic acids than terephthalic acid and isophthalic acid.

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) n -OH, where n is an integer from 3 to 6 (in particular propane-1,3-diol, butane-1,4 -diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic glycols having up to 6 carbon atoms. Of the cycloaliphatic diols, cyclohexanediols (especially cyclohexane-1,4-diol) are preferred.

Other cycloaliphatic dicarboxylic acids are, for example, cyclohexanedicarboxylic acids, in particular cyclohexane-1,4-dicarboxylic acid. Of the aliphatic dicarboxylic acids, the (C3 to C19) alkanedioic acids are particularly suitable, it being possible for the alkane part to be straight-chain or branched.

If one uses polyesters with a lower content of ethylene isophthalate-derived units than 2 wt .-%, the melting point of the film is too high. By using polyesters having a content of ethylene isophthalate-derived units higher than 15% by weight, the aroma barrier and migration properties (water vapor, gas barrier) of the film deteriorate. In addition, the deteriorate mechanical properties of the film, which is z. B. in a deteriorated processability of the film noticeable (for example, it tears easier).

Optionally, the base layer may consist of a mixture of polyethylene terephthalate and polybutylene terephthalate. The mixture contains 70 to 85% by weight of ethylene terephthalate and 15 to 30% by weight of butylene terephthalate-derived units. The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as described above. The sum of ethylene terephthalate-derived units and butylene terephthalate-derived units is at least 95% by weight of the polyester. Disadvantage of this mixture is that the two polyester transesterify in the extruder and the degree of transesterification is difficult to control.

The preparation of the polyester may, for. B. carried out after the transesterification process. It is based on dicarboxylic acid diols and diols, which are reacted with the usual transesterification catalysts such as zinc, calcium, lithium, magnesium and manganese salts. The intermediates are then polycondensed in the presence of commonly used polycondensation catalysts such as titanium salts. The preparation can also be carried out by the direct esterification process in the presence of polycondensation catalysts. It starts directly from the dicarboxylic acids and diols. Polyesters of the invention are available as commercial products.

The classical catalysts for the production of polyesters are still antimony compounds. Some antimony compounds may have a harmful effect, especially in higher concentrations and with frequent exposure. Therefore, in the EU, the maximum allowable migration of antimony from a film to a food is limited. At high temperatures and amorphous polyesters, as they are present after melting the film on a sheet, the antimony migration is increased and therefore a reduction of the antimony content is desirable. Antimony of polyethylene terephthalate (PET) is discussed in the trade press as questionable (eg W. Shotyk and M. Krachler in Environ. Sci. Technol., 2007, 41 (5), pp. 1560-1563 ).

The reason that antimony compounds are still used as polycondensation catalysts in polyester films is likely to be that antimony-free films have a significantly lower temperature stability than antimony-containing films and thus can not be used for high temperatures.

When laminating polyester film to metal, temperatures that are higher than the melting temperature of the film occur. Under these conditions, titanated polyesters undergo significant molecular weight degradation. As a result, micro-cracks occur during processing of the laminated sheet, which can lead to corrosion of the metal. The oven test described in the present specification correlates with molecular weight degradation and thus serves as a simple method of testing the suitability of the film for metal lamination. The thermal degradation titanium-catalyzed polyester can be counteracted as described below by the addition of stabilizers.

Amorphous topcoat A:

The amorphous cover layer A applied by coextrusion onto the base layer B comprises at least 19% by weight, preferably at least 23% by weight, particularly preferably at least 27% by weight, of ethylene isophthalate-derived units and up to 81% by weight. , Preferably 77 wt .-%, particularly preferably 73 wt .-% of ethylene terephthalate-derived units (in each case based on the total mass of polyester in the outer layer A). The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as they may also occur in the base layer.

Crystalline topcoat C:

For the other, crystalline cover layer C, it is possible in principle to use the same polymers as were previously described for the crystalline base layer B.

The cover layer C is filled to improve the winding behavior and the processability with inert particles. The concentration of the inert particles in the cover layer C is 0.05 wt% or more, preferably 0.10 wt% or more, and more preferably 0.15 wt% or more. The concentration of the inert particles in this layer should be less than or equal to 0.5% by weight, based on the total mass of the Layer, since otherwise deteriorates the producibility of the film. It depends essentially on the optical properties of the film to be achieved.

In a preferred embodiment, the entire film contains polyesters prepared with titanium-based catalysts and 50-10000 ppm of a radical scavenger, the content preferably being between 100-5000 ppm and especially between 150-1200 ppm. Lower levels than 50 ppm tend to result in failure in the oven test, and higher than 10000 ppm have no further improving effect on the film and therefore only reduce the economy and may lead to migration of the stabilizer from the film to a packaged food. Contents above 1200 ppm also tend to lead to the formation of gels with a high stabilizer content and a yellowish tinge.

In the outer layer C of the film, the proportion of radical scavenger is at least 300 ppm, preferably at least 500 ppm and ideally at least 800 ppm. Below 300 ppm, the oven test is failed.

Suitable radical scavengers are in the EP-A-2810776 described. Particularly good properties in terms of thermal stability, low migration from the film and yellowing showed the compounds with the CAS no. 1709-70-2, 3135-18-0, 6683-19-8 and 57569-40-1. These are preferred radical scavenger in the context of the invention. For the reasons mentioned, the compounds with the CAS no. 1709-70-2 and 6683-19-8.

coating

To improve the adhesion to aluminum, the film on the cover layer (A) is coated with a functional silane. Preferably, the functional group is a primary amine. The amino-functional silane is in the unhydrolyzed state by the general formula (R ¹ ) _a Si (R ² ) _b (R ³ ) _c wherein R ^{1 is} a non-hydrolyzable functional group having at least one primary amino group, R ^{2 is} a hydrolyzable group such as a lower alkoxy group, an acetoxy group or a halide, and R ^{3 is} an unreactive, nonhydrolyzable group such as a lower alkyl group or a phenyl group; where (a) is greater than or equal to 1; (b) greater than or equal to 1; (c) is greater than or equal to zero and a + b + c = 4. Lower alky or alkoxy groups are those having 1 to 4 C atoms and halides are fluorine, chlorine, bromine or iodine.

Examples of aminosilanes which obey this formula are N-2- (aminoethyl) -3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 4-aminobutyltriethoxysilane, 4-aminobutyldimethylmethoxysilane and p-aminophenyltrimethoxysilane. Preferred silane is N-2- (aminoethyl) -3-aminopropyltrimethoxysilane (CAS 1760-24-3).

In general, the aminosilane is hydrolyzed in water and applied to one side of the polyester film by a conventional method.

The coating solution is prepared by mixing the aminosilane with water at a level of from about 0.2 to about 6 weight percent. Optionally, to facilitate hydrolysis, a weak acid, e.g. Acetic acid, to achieve a pH of less than 6. In this case, at least one of the hydrolyzable groups of the silane is hydrolyzed to a silanol group (SiOH). The product of hydrolysis of the aminosilane is thought to have a partially hydrolyzed cyclic structure, with the amino group likely to undergo ionic bonding to the silicon portion of the molecule. Thus, the term hydrolyzed here may also refer to such teilhydrolysierte structures. The coating solution should be used no later than 6 hours after hydrolysis of the aminosilane to achieve a good result

The application of the coating on the amorphous cover layer A causes the film is no longer heat-sealable. Surprisingly, the adhesion to aluminum nevertheless improves.

The polyester film may be transparent, white or opaque, glossy or dull. These various optical properties are achieved, for example, by the addition of different amounts of additives such as barium sulfate, calcium carbonate, amorphous silica or titanium dioxide. These additives may be contained in both the base layer and the overcoat C.

Preferably, the film in the base layer contains a small amount (less than 2 wt .-%) of titanium dioxide. As a result, the film has a milky white appearance, whereby the occurring during sterilization blushing is less visible.

The inert particles used in the cover layer C for processing the film are preferably made of amorphous silica having a d50 value of 1-6 μm.

In the case of the film, the thickness of the amorphous covering layer A is in the range from 0.5 to 5 μm, preferably in the range from 0.6 to 3 μm, particularly preferably in the range from 0.7 to 2 μm. If the cover layer A is thinner than 0.5 μm, the metal adhesion is insufficient; if it is thicker than 5 μm, the film is too soft.

The total thickness of the polyester film of the invention may vary within certain limits. It is 5 to 20 microns, preferably 6 to 15 microns, more preferably 7 to 12 microns, wherein the layer B has a proportion of preferably 30 to 90% of the total thickness. If the film is thinner than 5 microns, the corrosion protection of the sheet is not given. If the film is thicker than 20 μm, this will adversely affect the economy of the laminated sheet.

After the oven test, the film according to the invention has an elongation at break in each film direction of more than 5%, preferably more than 10% and ideally more than 25%. Before the oven test, the elongation at break is over 60%.

Especially if the o.g. Radical scavengers are added in sufficient amount and further, when the most preferred stabilizers are used, the film according to the invention after the oven test, an increase in yellowness b * of less than 5, preferably less than 3 and ideally less than 1 on.

The film according to the invention usually has a shrinkage in the longitudinal and transverse direction of below 10%, preferably below 5%, and particularly preferably below 2%, at 150 ° C. As a result, a reduction in the width of the film during lamination is minimized.

In a particularly preferred embodiment, the amorphous topcoat A consists of 27% by weight of ethylene isophthalate-derived units and 72.96% by weight of ethylene terephthalate-derived units and 0.04% by weight of particles of amorphous silica having an average particle size (d50 ) of 2.5 μm. Furthermore, this cover layer A is provided with a coating which starts from N-2- (aminoethyl) -3-aminopropyltrimethoxysilane and has a thickness of 15 nm.

The base layer B consists of 4% by weight of ethylene isophthalate-derived units, 95.5% by weight of ethylene terephthalate-derived units and 0.5% by weight of titanium dioxide.

Topcoat C consists of 4 weight percent ethylene isophthalate derived units, 95.85 weight percent ethylene terephthalate derived units, and 0.15 weight percent amorphous silica particles having an average particle size (d59) of 2.5 microns.

All layers contain a radical scavenger in the concentration of 500 ppm (due to the small amount of radical scavenger this is not included in the 100 wt .-% of the respective layers).

Process for the preparation

The production process for polyester films is z. B. described in the Handbook of Thermoplastic Polyesters, Ed. S. Fakirov, Wiley-VCH, 2002 " or im Chapter "Polyesters, Films" in the "Encyclopedia of Polymer Science and Engineering, Vol. 12, John Wiley & Sons, 1988" , The preferred method of making the film includes the following steps. The raw materials are melted in one extruder per layer and extruded through a three-layer slot die on a cooled take-off roll. This film is then reheated and stretched ("oriented") in at least one direction, either in the machine direction (MD) or in the transverse direction (TD), but preferably in the longitudinal and transverse directions or in the transverse and longitudinal directions. The film temperatures in the stretching process are generally 10 to 60 ° C above the glass transition temperature Tg of the polyester used, the stretch ratio of the longitudinal stretching is usually 2.5 to 5.0, in particular 3.0 to 4.5, that of the transverse extension at 3 , 0 to 5.0, especially at 3.5 to 4.5. The longitudinal stretching can also be done simultaneously with the transverse extension (simultaneous stretching) or in each conceivable sequence sequence can be performed. This is followed by thermosetting of the film at oven temperatures of 180 to 235 ° C, in particular from 210 to 230 ° C. Subsequently, the film is cooled and wound up.

Advantages of the invention

The film according to the invention is distinguished by excellent adhesion to metal, in particular to aluminum. Furthermore, the film has good thermal resistance, i. a low degradation of the molecular weight at high temperatures as they occur during melting after lamination to sheet metal. In particular, the polyester-aluminum laminate is suitable for producing lids for beverage cans. The composition of the film ensures good deformability of the laminate and a clean tearing behavior of the lid.

The film shows good adhesion to aluminum even at relatively low process temperatures during lamination or melting, so that the mechanical stability of the aluminum is not impaired.

During the production of the film, it is ensured that the blend material (regenerated material) can be re-supplied to the extrusion in an amount of up to 60% by weight, based on the total weight of the film, without negatively affecting the physical properties of the film to be influenced.

properties

To characterize the raw materials and the films, the following measured values or measuring methods were used:

Glass transition temperature and melting point

The glass transition temperature and the melting point of the polyester of the outer layer A were determined using a DSC apparatus (Perkin-Elmer Pyris 1) ( DIN 53765 ). The sample was heated at 20 K / min to 300 ° C and 10 min. kept at this temperature. Thereafter, the sample was cooled as quickly as possible (500 K / min.) To 20 ° C. The sample was held at 20 ° C for 10 minutes and heated at 20 K / min to 300 ° C. In order to achieve better reproducibility, the values of the second heating were used.

Mechanical properties

Modulus of elasticity, tear strength, elongation at break and F5 value decrease in the longitudinal and transverse direction ISO 527-1 and 527-3 measured by means of a tensile strain gauge (type 010 from Zwick / DE).

Standard viscosity (SV)

The standard viscosity SV is - based on DIN 53726 - determined by measuring a 1 wt .-% solution in dichloroacetic acid (DCE) in a Ubbelohde viscometer at 25 ° C. From the relative viscosity (η _rel ), the dimensionless SV value is determined as follows: SV = (η _rel - 1) × 1000 Film or polymer raw materials were dissolved in DCE. The proportion of particles was determined by means of ash determination and corrected by appropriate extra scales.

shrink

The thermal shrinkage is determined on square film samples with an edge length of 10 cm. Samples are cut with one edge parallel to the machine direction and one edge perpendicular to the machine direction. The samples are measured accurately (the edge length L0 is determined for each machine direction TD and MD, L0 TD and L0 MD) and annealed for 15 min at the specified shrinkage temperature (here 150 ° C) in a convection oven. The samples are taken and measured accurately at room temperature (edge length LTD and LMD). The shrinkage results from the equation: Shrink [%] MD = 100 · (L0 MD - LMD) / L0 MD Shrinkage [%] TD = 100 * (L0 TD-LTD) / L0 TD

oven test

A piece of film is placed in a convection oven, which was preheated to 180 ° C. The film is placed on a wire mesh (mesh size 0.25-2 cm). The film remains in the oven for 90 minutes at 180 ° C. Then the mechanical properties, the shrinkage, the color codes and the SV are determined as described.

Adhesion to aluminum

Aluminum sheet with Cr (III) pre-treatment is heated to 200 ° C and the film is laminated under pressure to this sheet. Thereafter, the laminate is heated to 250 ° C for 10 seconds. This material is then heated in contact with 3% acetic acid for 30 min at 100 ° C. Subsequently, a cross-cut test is performed on the film side DIN EN ISO 2409 carried out. The result is rated with grades from 0 (very good) to 5 (very bad).

Measurement of crystallinity

The crystallinity of the respective film side is determined from the ratio of the intensities of the bands at 1040 cm ^-1 and 1337 cm ^-1 in the ATR spectrum (ATR = Attenuated Total Reflection), the intensities being normalized to the band at 1117 cm ^-1 . The band at 1040 cm ^-1 is amorphous polyester; at 1337 cm ^-1 is attributable to crystalline polyester ( Polymer Letters Edition, Vol. 12 (1974), pp. 13-19 ).

For amorphous layers:

For crystalline layers applies

The measurement is carried out using an IR spectrometer IFS28 from Bruker (Karlsruhe, DE) using a diamond ATR crystal.

The recording of the ATR spectrum can be made directly on the coated film. It is assumed that the coating has no influence on the spectrum of the cover layer up to a thickness of 0.1 μm. If in doubt, the coating can be removed prior to recording the ATR spectrum.

color values

The color codes L *, a *, b * are measured with the Color-Sphere meter from Byk-Gardner (US) in transmission for the individual layers and the layer packages according to the Standard DIN 1674 respectively. ASTM D2244 measured. The geometry used is d / 8 with gloss, the measuring range is 400-700 nm, the spectral resolution is 20 nm, the type of light used is D65, the observer used is 10 °, the diameter of the measuring orifice is 30 mm.

In the following the invention will be explained in more detail by means of examples.

Examples

The following starting materials were used to prepare the film described below:
PET1 = polyester raw material of ethylene glycol and terephthalic acid and isophthalic acid, the proportion of isophthalic acid in the polymer being 4.5% by weight with an SV value of 812 and a DEG content of 1.2% by weight. (Diethylene glycol content as a monomer). Manufactured by PTA method. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate.

PET2 = polyester raw material of ethylene glycol and terephthalic acid and isophthalic acid, wherein the proportion of isophthalic acid in the polymer at 23 wt.% With an SV value of 820, a DEG content of 1.4 wt.% (Diethylenglykolgehalt as monomer) and a content of 5000 ppm Irganox 1010, CAS no. 6683-19-8 (manufacturer: BASF Switzerland). The addition of the Irganox 1010 was carried out at the beginning of the polycondensation. Manufactured by PTA method. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate.

PET3 = polyester raw material of ethylene glycol and terephthalic acid and isophthalic acid, wherein the proportion of isophthalic acid in the polymer at 33 wt.% With an SV value of 810 and DEG content of 1.4 wt.% (Diethylenglykolgehalt as monomer). Manufactured by PTA method. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate.

PET4 = polyethylene terephthalate raw material of ethylene glycol and terephthalic acid with an SV value of 825, a DEG content of 0.9% by weight (diethylene glycol content as monomer) and a content of 5000 ppm Irganox 1010, CAS no. 6683-19-8 (manufacturer: BASF Switzerland). The addition of the Irganox 1010 was carried out at the beginning of the polycondensation. Manufactured by PTA method. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate.

PET5 = polyethylene terephthalate raw material of ethylene glycol and dimethyl terephthalate having an SV value of 820 and DEG content of 0.9% by weight (diethylene glycol content as monomer) and 1.5% by weight of Sylobloc 46 silica pigment with a d50 of 2.5 μm. Manufactured by PTA method. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate.

PET6 = 10,000 ppm Irganox 1010, CAS no. 6683-19-8 (manufacturer: BASF Switzerland) incorporated by means of a twin-screw extruder in PET1. SV value of 695.

PET7 = polyethylene terephthalate raw material of ethylene glycol and dimethyl terephthalate with a DEG content of 0.9 wt.% (Diethylenglykolgehalt as monomer) prepared by PTA process. Catalyst potassium titanyl oxalate with 18 ppm titanium. Transesterification catalyst zinc acetate. Solid phase condenses to an SV value of 1100.

PET8 = 60% by weight titanium dioxide pigment with a d50 of 0.2 μm incorporated by means of a twin-screw extruder in PET7. SV value of 510. Example 1: Topcoat (A): 35% by weight PET3 60% by weight PET2 5% by weight PET5 Base layer (B): 90% by weight PET1 10% by weight PET4 Covering layer (C), mixture of: 80% by weight PET1 10% by weight PET4 10% by weight PET5

Coating on topcoat (A):

2.0% by weight of 3-aminopropyltrimethoxysilane in water 3-aminopropyltrimethoxysilane was slowly added with stirring to deionized water and stirred for 30 minutes before use.

The above-mentioned raw materials were melted in each case in one extruder per layer and extruded through a three-layer slot die onto a cooled take-off roll. The resulting amorphous prefilm was then first stretched longitudinally. The elongate film was corona treated in a corona discharge machine and then coated by reverse gravure coating with the solution described above. Thereafter, the film was dried at a temperature of 100 ° C and then transversely stretched, fixed and rolled up (final thickness of the film 12.0 microns, outer layers each 1.1 microns). The conditions in the individual process steps were: Longitudinal stretching: Temperature: 80-115 ° C Longitudinal stretching ratio: 4.0 Transverse stretching: Temperature: 80-135 ° C Transverse stretching ratio: 4.1 fixation: 2 s at 225 ° C

The thickness of the dry coating is 12 nm.

The properties of the film thus obtained are shown in Table 1.

Example 2

The procedure was as described in Example 1. The raw material composition was now as follows: Topcoat (A): 50% by weight PET3 45% by weight PET2 5% by weight PET5 Base layer (B): 96% by weight PET1 4% by weight PET6 Covering layer (C), mixture of: 86% by weight PET1 10% by weight PET4 4% by weight PET5

Coating on topcoat (A):

2.5% by weight of N-2- (aminoethyl) -3-aminopropyltrimethoxysilane in water. N-2- (aminoethyl) -3-aminopropyltrimethoxysilane was slowly added to deionized water with stirring and stirred for 30 minutes before use.

Film has a total thickness of 9.0 microns, the outer layers A and C are both 1.0 micron thick.

The thickness of the dry coating is 15 nm.

Example 3

The procedure was as described in Example 1. The raw material composition was now as follows: Topcoat (A): 50% by weight PET3 45% by weight PET2 5% by weight PET5 Base layer (B): 50% by weight PET1 50% by weight regenerated Covering layer (C), mixture of: 80% by weight PET1 10% by weight PET4 10% by weight PET5

Coating on topcoat (A):

2.5% by weight of N-2- (aminoethyl) -3-aminopropyltrimethoxysilane in water. N-2- (aminoethyl) -3-aminopropyltrimethoxysilane was slowly added to deionized water with stirring and stirred for 30 minutes before use.

Film has a total thickness of 9.0 microns, the outer layers A and C are both 1.0 micron thick.

The thickness of the dry coating is 15 nm.

Comparative Example 1

A 20 μm film was produced as described in EP-B-312304. The raw material composition was as follows:
Topcoat A: copolyester with 20% by weight of ethylene isophthalate and 80% by weight of ethylene terephthalate (84% PET2 + 16% PET1)
Base Layer B: 98 weight percent polyethylene terephthalate having an SV of 815 (such as PET7 but not solid phase condensed) and 2 weight percent antiblock masterbatch with silica (PET5).

The film was prepared as described in Example 1 but not coated.

The adhesion of this film to aluminum is not sufficient. If this film is used for a laminate with aluminum, the temperature during melting of the film must be so high that the mechanical strength of the aluminum is reduced. This laminate can thus no longer be deep-drawn and is unsuitable for the production of cans. Table 1: Properties of the films of the examples example 1 Example 2 Example 3 Comparative Example 1 Melting point in ° C 246 244 243 254 Adhesion to aluminum, cross-cut test 0 0 0 3 Crystallinity Topcoat A 3.3 3.5 3.5 3.4 Crystallinity topcoat C 1.1 1.1 1.1 0.9 Δ b * after oven test 0.3 0.4 0.6 0.5 SV after oven test 730 725 710 720 Elongation at break MD in% 91 93 89 95 Elongation at break TD in% 99 101 97 106 Elongation at break MD in% after oven test 90 91 90 94 Elongation at break TD in% after oven test 99 96 96 103

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• GB 1465973A [0006]
• EP 312304 B [0007]
• EP 474240 B [0008]
• EP 586161 A [0009]
• EP 2810776 A [0030]

Cited non-patent literature

• W. Shotyk and M. Krachler in Environ. Sci. Technol., 2007, 41 (5), pp. 1560-1563 [0022]
• Handbook of Thermoplastic Polyesters, Ed. S. Fakirov, Wiley-VCH, 2002 " [0048]
• Chapter "Polyesters, Films" in the "Encyclopedia of Polymer Science and Engineering, Vol. 12, John Wiley & Sons, 1988" [0048]
• DIN 53765 [0053]
• ISO 527-1 and 527-3 [0054]
• DIN 53726 [0055]
• DIN EN ISO 2409 [0058]
• Polymer Letters Edition, Vol. 12 (1974), pp. 13-19 [0059]
• Standard DIN 1674 [0064]
• ASTM D2244 [0064]

Claims (16)

Multilayer, biaxially oriented polyester film comprising a base layer B, a cover layer A and a cover layer C, characterized in that the cover layer A is amorphous, the base layer B and the cover layer C are crystalline and wherein the crystalline base layer B (based on the mass Polyester in the layer) contains from 2 to 15% by weight of isophthalate-derived units and the amorphous topcoat A (based on the weight of polyester in the layer) contains more than 19% by weight of isophthalate-derived units. Polyester film according to claim 1, characterized in that the cover layer A is provided with a silane-based coating. Polyester film according to claim 1 or 2, characterized in that the polyester of the base layer B to at least 85 wt .-%, preferably at least 90 wt .-%, particularly preferably at least 92 wt .-% consists of ethylene terephthalate-derived units (in each case based on the total mass of polyester). Polyester film according to claim 1, 2 or 3, characterized in that the polyester of the base layer B preferably consists of 3 to 10 wt .-%, particularly preferably 4 to 8 wt .-% of ethylene isophthalate-derived units. A polyester film according to any one of claims 1 to 4, characterized in that the sum of ethylene terephthalate-derived units and ethylene isophthalate-derived units is at least 95% by weight of the polyester. A polyester film according to claim 3, characterized in that the polyester of the base layer B consists of 70 to 85 wt .-% ethylene terephthalate and 15 to 30 wt .-% butylene terephthalate-derived units instead of the isophthalate and terephthalate-derived units. Polyester film according to one of claims 1 to 6, characterized in that the amorphous top layer A to at least 19 wt .-%, preferably at least 23 wt .-%, more preferably at least 27 wt .-% of ethylene isophthalate-derived units and up to 81 wt .-%, preferably 77 wt .-%, particularly preferably 73 wt .-% of ethylene terephthalate-derived units (in each case based on the total mass of polyester in the outer layer A). Polyester film according to one of claims 1 to 7, characterized in that the cover layer C 0.05 wt .-% or more, preferably 0.10 wt .-% or more and particularly preferably 0.15 wt .-% or more inert particles contains. Polyester film according to one of claims 1 to 8, characterized in that the polyesters of the film have been produced with titanium-based catalysts. Polyester film according to one of claims 1 to 9, characterized in that the film 50-10000 ppm, preferably 100-5000 ppm and in particular 150-1200 ppm of a radical scavenger and preferably the cover layer C at least 300 ppm, preferably at least 500 ppm and more preferably contains at least 800 ppm of radical scavenger. Polyester film according to claim 10, characterized in that the radical scavenger is selected from one or more of the compounds with the CAS no. 1709-70-2, 3135-18-0, 6683-19-8 and 57569-40-1, in particular CAS no. 1709-70-2 and 6683-19-8. Polyester film according to one of claims 1 to 11, characterized in that the cover layer (A) is coated with a functional silane, which is preferably an amino-functional silane, which particularly preferably in the unhydrolyzed state, a compound of formula (R ¹ ) _a Si (R ² ) _b (R ³ ) _c wherein R ^{1 is} a non-hydrolyzable functional group having at least one primary amino group, R ^{2 is} a hydrolyzable group such as a lower alkoxy group, an acetoxy group or a halide, and R ^{3 represents} an unreactive, nonhydrolyzable group such as a lower alkyl group or a phenyl group; a is greater than or equal to 1; b is greater than or equal to 1; c is greater than or equal to zero and a + b + c = 4 and lower alky or alkoxy groups are those having 1 to 4 carbon atoms and halides are fluorine, chlorine, bromine or iodine. Polyester film according to one of claims 1 to 12, characterized in that it is 5-20 μm thick. A process for producing a polyester film according to claim 1, wherein first of all the polyester blends of the layers A, B and C are compressed and liquefied in a plurality of extruders, the melts are formed in a multi-layer die into a flat melt film which is then deposited on a chill roll and one or more Withdrawing rollers is withdrawn as a prefilm, wherein this cools and solidifies and then biaxially oriented and optionally coated on the outer side A, characterized in that the base layer B and the outer layer C are crystalline and the base layer B (based on the mass Polyester) contains from 2 to 15% by weight of isophthalate-derived units and the amorphous topcoat A contains (based on the mass of polyester) more than 19% by weight of isophthalate-derived units and wherein the topcoat A is optionally silane-based Coating is provided.  Use of a film according to any one of claims 1-13 for lamination with sheets, which are preferably used for the production of lids for beverage cans.  Use according to claim 15, wherein the sheet is an aluminum sheet.